The topic of this proposal is applicable to Research Objectives 7 and 23 in PAR-03-056. The goal of this NIA pilot grant is to develop and characterize transgenic mouse lines that constitutively overexpress either wildtype or mutant ubiquitin in the aging central nervous system (CNS). We recently found that a reduction in the level of free ubiquitin following various neurotoxic insults leads to an accumulation of the pro-apoptotic protein, p53, and selective neurodegeneration. This novel cell death pathway is also associated with increased expression of a mutant form of ubiquitin, termed Ub+l, caused by a post-transcriptional frameshift in ubiquitin mRNA. By impairing ubiquitination and disrupting proteasome function Ub+l promotes additional protein accumulation and cell death. Both impaired ubiquitin-proteasome function and protein aggregates containing Ub+l have been demonstrated in Alzheimer's and other neurodegenerative diseases. However, the exact nature of the relationships between formation of Ub+l by "molecular misreading", abnormal ubiquitin-proteasome function and neuronal cell death remain poorly understood. We therefore propose to develop transgenic mouse lines that overexpress either free wild-type ubiquitin or mutant Ub+l in CNS neurons. Transgene expression will be directed by a Thyl promoter which is neuron-specific. An additional and highly beneficial feature of this expression system is that the Thyl promoter is inactive during embryonic and early postnatal life, thereby avoiding potentially adverse or confounding effects of transgene expression during early stages of development. Phenotypes will be characterized according to gross and microscopic neuropathology, apoptotic gene expression and the degree of cell death at different ages and in different brain regions. The immediate benefits provided by these mice will include establishing clinical relevance for the accumulation of Ub+l in age-related neurodegenerative diseases, and determining whether increasing the available pool of free ubiquitin is neuroprotective following adverse stimuli. Future applications will employ ubiquitin transgenic mice in high throughput screening studies to identify ubiquitin-modulating pharmacological agents for age-related neurodegenerative disorders such as Alzheimer's disease.